This started out as an Airtripper extruder, but I decided to tweak the design to better fit my printer and the parts I had on hand, and by the time I was finished it was nearly unrecognizable.
Changes made from the original Airtripper design include:
Moving the mounting surface to be on the face that the filament enters the extruder through. This was more convenient for mounting the extruder vertically, with the filament coming down from above.
Redesigning the extruder to use bearings I had on hand. This included a 525 bearing for the motor axle support, and a 1614RSbearing for the pinch arm.
I replaced the Bowden tube clamp with a low-profile design I came up with that uses three bolts to compress a tightening cone around the tube. It doesn't require printing threads and seems to take up less vertical space than other designs I've seen.
Finally, I'm a shoulder bolt and two R4RS bearings to support the pinch arm pivot. This was an experiment I did only to use up some parts that had been in my junk bin for years. In retrospect it was completely unnecessary, actually makes the extruder harder to assemble, and was kind of a dumb idea.
Plans for the extruder, and all the other parts I've printed for the printer so far, have been uploaded as Thing 31889 on Thingiverse. I upload these only for reference purposes. I don't actually recommend printing any of them as they are. I've found design issues with all these parts as I've built the printer and am preparing a complete set of redesigned parts.